Drugs are generally screened according to electrical activities of the cell as an index by a patch clamp method or a method using a chemical, such as a fluorochrome or luminescence indicator. In the patch clamp method, a micro-electrode probe electrically records an ion transportation through a single channel of a protein molecule at a micro-section called “patch” of cell membrane attached to a tip of a micropipet. This method is one of the few methods that can evaluate functions of a protein molecule in real time. (Refer to “Molecular Biology of the Cell” third edition by Garland Publishing Inc. New York. 1994, written by Bruce Alberts et al. Japanese Edition “Molecular Biology of the Cell” pages 181-182, published from Kyouikusha Inc. 1995)
A fluorochrome or luminescence indicator which emits light in response to a change of a density of a specific ion monitors migration of the ion in a cell, thereby measuring the electrical activities of the cell.
The patch clamp method requires expertise for producing and operating the micropipet, and requires a long time to measure one sample, thus not being suitable for screening a large number of chemical-compound candidates. The method using the fluorochrome or the like can screen a large number of chemical-compounds candidates fast, but requires dyeing cells. A background of the cells may be colored due to pigment in measuring, and is decolorized according to a lapse of time, thus reducing an S/N ratio.